af_join: switch to an AVOptions-based system.

Change the mappings separator from comma to '|' to avoid excessive
escaping, since comma is already used for separating filters in the
filtergraph description.
lavfi/biquads: switch to an AVOptions-based system

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Merge commit 'dd7fc37c71955b78a2687f29e871f714d18de386'

* commit 'dd7fc37c71955b78a2687f29e871f714d18de386':
  af_join: switch to an AVOptions-based system.

Conflicts:
	doc/filters.texi
	libavfilter/af_join.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'richardpl/biquads'

* richardpl/biquads:
  lavfi/biquads: switch to an AVOptions-based system

Merged-by: Michael Niedermayer <michaelni@gmx.at>